The invention relates to a drive device having an electric drive motor, having a casing, and at least one shaft driven by the drive motor, with compensating means with which an adjustment of or compensation for end play of the shaft can be made when installing the shaft, and with securing means with which the shaft is secured after end play has been adjusted or compensated for. The invention also relates to a method of installing a drive device of this type.
The shaft driven by the drive motor is understood to mean in what follows an output shaft driven by the drive motor through a gear, specifically through a worm gear, as well as an armature shaft driven directly by the drive motor.
Drive devices of this type find an application particularly in the automotive industry as servo motors for seat adjusters, steering column adjusters, window regulators, sliding sunroofs or similar, and as drive devices for windshield wiper systems. The drive devices normally have a worm gear attached to the drive motor, which advantageously has small dimensions, can transmit high levels of power and is self-locking.
Specifically because of the tapered flanks of the worm and the worm wheel in a worm drive of this type, an axial force acts on the armature shaft of the drive motor during operation of the drive device, as well as on the output shaft of the worm drive. The direction of the axial force depends on the direction of the armature shaft rotation. With a change in direction of the drive motor or a change in external load, the direction of the axial force on the armature shaft as well as on the output shaft is reversed. During the installation of a shaft of this type, it is of special importance to adjust the end play precisely, or to compensate for the end play, so that the shafts is carried free of end play. If the shaft of drive devices of this type are installed with end play, abrupt starting motions and irritating noises result when the drive motor reverses direction. Furthermore, noticeable relative motions can result if the servo motor is employed as a seat back adjuster, for example. The person occupying the particular seat perceives the end play as relative movement of the seat back, even when the motor of the drive device is not running. This phenomenon is additionally known in the case of steering column adjusters. End play that is present can additionally lead to uneven loading on the shaft, and on the worm and worm wheel, causing malfunctions of the drive device.
A generic drive device is known from DE 198 24 382 A1 in which the end play is adjusted during assembly by means of a pin projecting from the housing of the drive device. A pin of this type is then swaged to the housing after the end play is adjusted.
The prior art of this type has the disadvantage that compensation for, or adjustment of the end play is complicated to perform. An extra device is required which exerts a force from the outer side of the housing on the end bearing carrying the shaft by way of the corresponding pin. In addition, because of the opening extending through the housing to receive the pin, problems can arise with the sealing of the worm drive.
The object of the present invention is therefore to eliminate the disadvantages of the previously enumerated disadvantages of the prior art.